This proposal seeks a renewal of funding for the United States based International Breast Cancer Study Group (IBCSG) Statistical and Data Management Center, a resource that contributes to International -US collaboration in the following areas: Access to the IBCSG clinical database of 22,475 breast cancer patients enrolled in large-scale, randomized clinical trials with up to 26 years maximum follow-up; Access to the IBCSG tissue bank database for over 2000 patients with 10-20 years median follow-up; Expertise of statistical and medical investigators and collaboration in the IBCSG research agenda. This resource gives NCI an opportunity to significantly improve our understanding of treatment and prognosis of women with operable breast cancer. Participation of the IBCSG in US trials and enrollment of US patients in IBCSG trials, are essential to accrue the large number of patients needed to make real progress, especially in trials assessing treatments in relatively rare patient populations (e.g., very young women). As our understanding of the pathogenesis of breast cancer and targeted treatment responsiveness increases, the need for tailored treatment investigations focusing on more homogeneous patient cohorts also increases. Support of this proposal to continue the successful IBCSG-NCI partnership will result in enhancing the effective use of improved endocrine therapies, defining the role of chemotherapy for older and younger women, assessing maintenance metronomic chemotherapy following standard cytotoxic treatment, and evaluating chemotherapy after loco-regional recurrence. The long range goal of the IBCSG is to determine the best possible treatments for operable breast cancer. The specific aims of this application comprise the major areas of research toward this goal: To provide US-based statistical and data management collaboration for the design, conduct, analysis, and reporting of IBCSG randomized clinical trials evaluating adjuvant therapies; To facilitate correlative research by providing access to out uniformly treated and followed populations of patients with tissue collection at diagnosis; To facilitate collaboration on database studies to identify and confirm the relationship between characteristics of breast cancer patients and/or tumors and response to adjuvant therapies; To enhance collaboration between the IBCSG and US cooperative groups in the area of quality-of-life evaluation for patients with breast cancer.